Chemical-looping combustion of biomass was carried out in a 10 kW th reactor with iron oxide as an oxygen carrier. A total 30 h of test was achieved with the same batch of iron oxide oxygen carrier. The effect of the fuel reactor temperature on gas composition of the fuel reactor and the air reactor, the proportion of biomass carbon reacting in the fuel reactor, and the conversion of biomass carbon to CO 2 in the fuel reactor was experimentally investigated. The results showed that the CO production from biomass gasification with CO 2 was more temperature dependent than the CO oxidation with iron oxide in the fuel reactor, and an increase in the fuel reactor temperature produced a higher increase for the CO production from biomass gasification than for the oxidation of CO by iron oxide. Although the conversion of biomass carbon to CO 2 in the fuel reactor decreased with the increase of the fuel reactor temperature, there was a substantial increase in the proportion of biomass carbon reacting in the fuel reactor. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were utilized to characterize fresh and reacted oxygen carrier particles. The results showed that the transformation of Fe 2 O 3 to Fe 3 O 4 is the favored step in the process of iron oxide reduction with biomass syngas. The low reactivity of reacted oxygen carrier was mainly ascribed to the sintering grains on the particle surface. To restrain the surface sintering of oxygen carrier particles, an intensive oxidization of reduced oxygen carrier with air in the air reactor should be avoided in the process of oxygen carrier regeneration, and air staging should be adopted for the oxidization of reduced oxygen carrier with air in the air reactor.

Chemical looping combustion (CLC) is a new innovative technology with inherent separation of CO2 without energy penalty. Experiments on chemical looping combustion of biomass/coal were conducted in a 1 kWth continuous reactor, and an Australia iron ore was selected as oxygen carrier. Both biomass/coal mixture and biomass were used as fuels. The effect of temperature on gas composition of both the fuel reactor and the air reactor, conversion efficiency of carbonaceous gases, carbon capture efficiency, and oxide oxygen fraction was investigated. An increase in the fuel reactor temperature produced a higher CO2 concentration in the fuel reactor for biomass/coal mixture, whereas it produced a lower one for pure biomass. CO concentration in the fuel reactor increased in both fuel conditions. Due to the poor oxygen transport capacity and the thermodynamic constraint of the iron ore conversion from Fe2O3 to Fe3O4, a higher temperature would contribute to decreasing the conversion efficiency of carbonaceous gases for both biomass and biomass/coal mixture. Both carbon capture efficiency and oxide oxygen fraction were enhanced with increasing the fuel reactor temperature, and the deviation between them was caused by the combustible carbonaceous gases in the fuel reactor. Both the fresh and the used oxygen carrier particles were characterized. X-ray diffraction (XRD) results indicated that the iron ore as oxygen carrier possesses a good regenerable ability in the CLC process. This is attributed to the existence of quartz in the iron ore particles and its sintering inhibition. Reactions between SiO2 and Fe3O4 may occur at a high temperature under a reducing condition. Scanning electron microscope (SEM) analysis showed that as a consequence of accumulative effect of redox reaction and thermal stress, the used oxygen carrier particles obtained a porous structure facilitating the gas−solid reactions. Energy dispersive X-ray (EDX) results demonstrated the deposition of alkali metals on the particle surface of oxygen carrier during the CLC process of biomass. Blending biomass with coal and adding some additives might be effective measures to reduce the potential negative influence of biomass ash on oxygen carrier.

This review article focuses on the challenges and opportunities of biomass-based chemical looping technologies and explores fundamentals, recent developments and future perspectives.

Fast pyrolysis of cellulose, xylan, and lignin was experimentally conducted between 350 and 650 °C in a tube furnace, and the effect of temperature on pyrolysis products (char, noncondensable gas, and bio-oil) was investigated. The yields of char, noncondensable gas, and bio-oil were quantified using gas chromatography and gas chromatography with mass spectrometry. The noncondensable gas mainly consists of CO, CO 2 , CH 4 , and H 2 . The bio-oil includes acids, ketones, aldehydes, esters, benzenes, alcohols, alkenes, phenols, alkanels, carbohydrates, etc. The results show that cellulose is the principal source of carbohydrates and phenols are the basis of the bio-oil from lignin, while the bio-oil from xylan mainly consists of acids, ketones, aldehydes, and phenols. The char yields for the three components decrease with an increase in temperature, and the gas yields and bio-oil yields increase with an increase in temperature, reach a maximum at a certain temperature, and then decrease after that temperature. The maximum biooil yields for cellulose, xylan, and lignin are 65, 53, and 40%, respectively; and their corresponding temperatures are 400, 450, and 500 °C, respectively. To investigate a relationship between biomass and three major components (hemicellulose, cellulose, and lignin), the pyrolysis of three typical biomass samples (rice straw, corn stalk, and peanut vine) was also studied, and the additivity law is adopted to predict the product components of biomass pyrolysis based on the content of hemicelluloses, cellulose, and lignin. The results show that the additivity law can predict reasonably the trend of product yields of biomass samples from their composition of hemicelluloses, cellulose, and lignin.

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